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978-3-8439-2353-8, Reihe Organische Chemie
Visible light mediated photoredox catalysis: reductive carbon-carbon bond forming reactions
118 Seiten, Dissertation Rheinisch-Westfälische Technische Hochschule Aachen (2015), Softcover, A5
This dissertation described firstly the ‘disfavoured’ 5-endo-trig cyclization of several alpha-chloroamides, all of which employ visible light photoredox catalysis and proceed via the homolysis of the C(sp3)-Cl bond. The importance of alpha-chloroenamides as radical precursors was underlined by the fact that, applying the same conditions to alpha-bromo and iodoenamides, low conversion to the desired product was observed in favor of other side- products. The reaction proved successful in the synthesis of gamma-lactams in moderate to good yields and with remarkable high diastereoselectivity.
The second part of this dissertation concerned the photoredox catalyzed umpolung reactions of carbonyl derivatives. In first place, we studied the ketyl-olefin cyclization which was applied to the synthesis of a variety of substituted 3-benzylchroman-4-ols in good to excellent yields. We demonstrated that aldehydes are suitable substrates for the ketyl formation, highlighting a brand new activation mode wherein amines played the dual role of electron and proton donors. The scope could also be extended to the ketyl-alkyne coupling with satisfactory results.
Lastly, the photoredox cycle was applied to the coupling of two alpha-amino radicals, the first generated by one electron reduction of imines, and the second obtained by one electron oxidation of amine. Notably, the addition of an inorganic base was essential for the reaction to proceed until full conversion.